Machine for cutting double-helical or double-spiral gears



A ril-23, 1929. P. BOTTCHER MACHINE FOR CUTTING DOUBLE HELICAL O R DOUBLE SPIRAL GEARS Original Filed July 31, 1925 2 Sheets-Sheet 1 l'mreni'ar: 317646949! 1 p. Q RI- 1,709,835

GIL [NB FOR CUTTING DOUBLE HELICAL OR DOUBLE SPIRAL'GEARS z n l Filed y 1, 1925 2 Sheets-Sheet 2 In vntar ,gzwezao WMi Patented Apr. 23, 1929..

UNITED STATE-S 1,709,835 PATENT OFFICE.

m. BtS'rroHEn, OF'ALTONA-BAHRENFELD, NEAR HAMBURG, GERMANY.

"mA'cHInE non cu'rcrrne DOUBLE -HELICAL on DOUBIiE-SIPIRAL GEARS.

Original application filed July 31, 1925, Serial No. 47,355, and in Germany September 12, 1924. Divided i and this application filedOctober 25, 1926. Serial- No. 144,086.

This invention relates to themanufacture of double helical or double spiral .gears, sometimes referred to as herringboi ie gears, including cylindrical and bevel pinions and wheels, the object being to produce teeth for such gears having a new and etlicient configuration, andals'o to facilitate the manufacture thereof.

The high efficiency and practical advantages of herringbone gears are well known in the art bdth as regards cylindrical and bevel gears, inclmlingwheels and pinions. It is obvious that maximum efficiency can only be obtained if the two inclined branches of each tooth merge-into each other, that is to say, they are continuous. in the theoretically true herringbone tooth a sharp corner occurs at the junction of the two branches ofthe tooth but this presents ditliculties in practice and frequently the corner is rounded off bya subsequent or secondary operation. v y

\Vhen' herringbone gears are cut from blanks according to the profiled end mill system the teeth so formed have the defect that the two branches of each tooth do not intersect sharply as the radius of the end mill results in a corresponding rounding on the concave side at the junction and, in

order to ensure accurate meshing of this rounded portion with the corresponding v point ,or apex of the teeth of a fellow wheel, it is necessary in a subsequent operation to round the apex .or convex side of the junction-to correspond.

As a profiled end mill does not produce a correct profile for this rounded portion at the junction this part cannot participate in the transmission of power, so that the effective width of the tooth is diminished;

A herringbone tooth formed by an end mill, therefore, comprises two inclined branches united by a small circular arcuate portion, corresponding to the radius of the end mill, sothat the herringbone formation to some extent curved, but it does not have a bearing surface atthe curved portion. In order to avoid the above defects it has been proposed to substitute circular arcuate teeth for the herringbone teeth. If a tooth of this form be arrangedsymmetrically in relation to the median plane of the wheel it not built up as it were from two diflicultly united branches and can be machine cut in a continuous operation. Such teeth therefore prefor the entire tooth. are usually made broader than herringbone sent no serious difliculties in machining according to the modern generating methods, and moreover each tooth presents a bearing surface throughout the entire width of the wheel, avoiding an inconvenient corners. Such teeth, like the herringbone teeth, also ensure gradual transmission of power without. setting up axial pressure. v

In comparison with the herringbone teeth, other conditions being equal, the circular arcuate teeth have the disadvantage of a much reduced overlap owing to their very slight inclination to the median plane of the wheel, what inclination there is increasing gradually towards the edges of the wheel rim and resulting in a comparatively small overlap Such wheels therefore toothed wheels for the same conditions.

The object of the present invention therefore is to obtain a configuration of tooth intermediate in some respects of the two configurations above discussed, which will retain advantages of the circular arcuate teeth essentially the easy and accurate machining of them by generating while substantially eliminating their disadvantages, particularly as regards overlap.

The fundamental principle of a continuous curve is retained, but is modified or adapted, that is the simple circular arc of uniform curvature throughout is replaced by a curve which approaches more nearly tothe herringbone configuration, and-is therefore much more efficient. For example: by shaping the tooth according to a hypocycloid it is possible to generate a tooth of a form similar to the nu-abolicform.

The unitary connection of the parts of the whole tooth on a continuous curve is therefore maintained, while the overlap is considerably increased in comparison with tration is adopted as the outlines shown 'are i assumed to be produced by the molding or cutter generating process wherein thecutting edge of the tool is moved in the plane (in which the sections are assumed tobe developed) in order to cut or carveout the desired shape of tooth from a blank rotated or rolled in this plane, as will belclear to. those skilled in the artofgear' cutting,"the outlines shown in the figures. definingithe flanks of the teeth in this plane,'rep resent-- -ing at the same time the path of'the cutting edge when producing the teeth erating process. I

Figure 2 is a developed section of one form ot tooth according to the invention suitable for a bevel wheel.

Figure 3 is a perspective view illustratby the gening two double helical gears according to" the invention.

Figure 4 is a perspective view illustrating one form of double helical bevel pinion and bevel Wheel according to the invention.

Figure 5 is a side elevation partly in section of the cutting tool and the work.

Figure 6 is a top plan view, ofFigure 5.

Figure 7 is a diagram showing the locus of bevel Wheels the required profile of a tooth of a crown wheel, namely, one having rectilinear teeth) the helical or spiral paths for the tools being generated by the setting up of a certain relative motion between the 'blank and cutter, usually by rotating the blank about its axis simultaneously with the movement of the tool carrier. The profile of the teeth produced with machines of this kind is therefore dependent upon the cutting movement of the cutting edge of the tool being generated from the teeth of a rack or of a crown wheel as basis.

A tool carrier and-its operation will be hereinafter) described by way of example adapted to move one or more obliquely set cutting edges in such a manner as to produce a curve of the kind above described, in accordance with the generating method. This movement may be produced in difi'erout ways, for instance by theuse of suitable templets adapted to influence or modify the cutting movement of the cutting edges.

Devices may be usedhowever which are so constructed as to produce a cutting move- M Y f 1,709,835?

ment along the desired curvefbyijthe coin binat'ion of several simple motions," for 'l!lstance rectilinear or rotary motlons Wlth:

. out necessitating the use, of 'templets. This method is also adaptable to various com binations, inasmuch as with this method the exact shape of the curve is not sharply prescribed, but is subject. to variation Within the limits hercinbefore indicated with the object in view. Thus, a plurality of mo tions derived from a simple rotary motion and oscillating on a straight line OI Oil a circular arc may be combined with one another or with simple rotary motionsp Further, a plurality of simple rotary motions may be combined to produce, the desired cutting movement. In such a. method'ot operating, several simple motions are utilized to cause the cutter to follow a curve of the kind above described opposite to the wheel blank, each participating in one of the motions. i

The various possible constructions, however, do not per se constitute thesubject of the invention, and the description of one example of tool carrier will therefore be suflicient to illustrate the idea of the invention.

A comparatively simple solution of the problem is the production of the cutting movement by the compounding of two simultancously acting rotarymotions. If two rotary motions about different axes are simultaneously imparted to the carrier of the cutting tools, it will perform a planetary movement. A tool carrier of this kind having aplanetary movement-fin plageof the simple, rectilinear or rotary movement, and

itsposition in relation to the blank is shown. diagrammatically Iin ,Figlire 8 partly in section, and in Figuregiliin' .1 l .j j p The main shaft 1 is providedga neot its ends with a driving pulley 2' H d'-.with a crank pin at its other end, iid is journaled in a-fram'e 4. Atool carrier 5 having a' gearwheel 6 is 'rotatablyfmounte'd onthe crank pin 3. One end ofxthe name a is extended to.,;fo rm a stationary ternal gear wheel 7 meshing with the gea heel 6 of the tool carrier-5. Four cutting tools 8, 9, 10- and 11 having straight fianks-and corre sponding to the profile of the half tooth of a rack are provided on the tool-carrier 5, the tools being arranged in diametrically opposed pairs and all equidistant from the centre of crank pin 3. Upon'rotating the main shaft 1 by the pulley 2 the axis of the crank pin 3 will describe a small circle a with the radius of its eccentricity. The tool. carrier 5 which is rotatably mounted upon "the pin'3 will'take part in this rotation of themain shaft 1, while, however, at the same time rotating in the opposite direction about the crank pin 3 in consequence ofthe revolution of its gear wheel 6 on the stashown in Figure 10. The two gear wheels 6 and 7 shown in Figures 8 and 9 and rolling one within the other are indicated by the circles K and K in Figure 10. The path described by each cutting edge corresponds to the locus of a point P connected to the rolling circle K at a distance R from the centre of the circle K The rolling circle K is assumed to roll in the relatively stationary circle K without sliding relatively thereto. The centre M of the rolling circle K will thereby be caused to describe a circle of the radius R around the centre M of the stationary circle K The point P, will describe a continuous hypocycloid.

Provided thediameters of the circles K and K bear the ratio to each other of 4:5, the point P will describe a hypocycloid by the rolling of the circle K within the circle K whichhypocycloid will possess the shape of a rounded pentagon. The section of thispentagon' which is shown in full lines is of the desired substantially parabolic or herringbone shape and in the same manner as a circular are it may be used directly as the fundamental form developed in .a plane,

. for the novel form of herringbone teeth according to this invention.

The exact shape of the prolonged hypocycloid produced is determined by a corresponding selection of the proportions of dimensions between the values R K and K In the operation ofsuch tools it is immaterial whether the single movements are effected continuously in the same direction of rotation or only a sufiicient part of the curve is described in the generation of the tooth and then a reversal in the direction of move ment is effected so that the cutting tool reciprocates or oscillates along the curve of the tooth like a planing machine.

' Similar results, that is to say, cutting movementsalong curves, similar to parabolas may also be obtained, however, by means of other tool carriers of different construction and it should be understood that the invention does I not refer to the particular details of conto which'have merely been discussed with reference to an embodiment of the principles of the invention by way of example and as an illustration of the facility of manufacture of the subject matter of the invention, the invention referring in its broad aspects to structions of machines of the kind referred the method or process ofmanufacturingthe new shape of herringbone teeth.

It is to be understood that the invention is not restricted to details of construction and-arrangement of parts exceptas may result from the terms of the claims hereunto appended.

I claim: I I

1. In a method of cutting the teeth of a herringbone toothed wheel of the cylindrical or bevel wheel t' pe by moving a cutter along the flanks 'of t e teeth of a rack or of a crown wheel and generating the helical formation by a relative generating movement between the blank and the tool holder, imparting to the tool a cutting'movement along a curve of approximately'parabolic form by imparting to thecutting tool two simultaneously acting simple rotary motions about different axes adapted to impart a plai' etary cutting movement along an epi-trochoid of substantially parabolic form.

2. The method of cutting the teeth of a herringbone toothed wheel of the cylindrical or bevel wheel type by moving a cutter along the flanks of the teeth of a rack or of a crown 1 wheel and generating the helical formation by a relative generating movement between the blank and the tool holder, said relative-movement being the resultant of the movement of the cutting tool about two spaced axes, said rotary movements being continuous and in the same direction.

The foregoing specification signed at Hamburg, this eighth day of October, 1926.

PAUL BOTTGHER. 

